4 Dr. Boase's Remarks on Mr. Hopkins's 



several definite rays, among which two green rays appeared 

 to me to possess nearly the same tint, although differing in 

 refrangibility. 



Gold-leaf, and copper-leaf each afforded a fine spectrum 

 exhibiting peculiar definite rays. The effect of zinc was still 

 more interesting ; I observed in this instance a strong red ray, 

 three blue rays, besides several more of other colours. These 

 experiments were made in the laboratory of the Royal Institu- 

 tion in June 1834. 



Errata. In the memoir on Light, vol. v. p. 326, line 22, 

 for " jointed" read " joined." 



P. 328, line 3 from the hoiiom, for " observations" read 

 " obscurations". 



The conclusion of the article in vol. iv. p. 290, is inaccu- 

 rately expressed ; it should stand thus : " But when the obli- 

 quity reaches a certain point one of the images suffers total 

 internal reflexion before the other does. This would equally 

 happen whether the balsam were employed or not: but its 

 use is attended with advantage because this effect then takes 

 place at a much greater angle of obliquity, and consequently 

 the separation of the images is more perfectly and conveni- 

 ently obtained." 



II. Beynarlcs on Mr. Hopkins's " Researches in Physical Geo- 

 logy" By Henry S. Boase, M.D.^ S^c.y Secretary to the 

 Royal Geological Society of Cornwall.^ 



THE vast accumulation of facts during the present cen- 

 tury concerning the structure of the earth, has esta- 

 blished the title of geology to rank among the more important 

 branches of human knowledge : and the attempts which have 

 been lately made to solve geological problems by mathemati- 

 cal analysis, lead us to expect that it may one day attain to a 

 more exalted position among the sciences. In Germany, this 

 application was made many years ago, more particularly by 

 Schmidt and Zimmermann, in illustration of the phaenomena 

 of veins. And in France, Elie de Beaumont and Dufrenoy 

 have called in its aid to support the doctrine of elevation-cra- 

 ters. But to Mr. Hopkins we are greatly indebted for vindi- 

 cating the character of the science in this country by making 

 a more extended application of this agent, and for the im- 

 portant results at which he has arrived f. 



« Communicated by the Author. 



t Mr. Hopkins's Abstract of his Memoir on Physical Geology appeared 

 in our last volume, p. ii27, cl acq. 



